Arizona Public Service Company and its partner GreenFuel Technologies were recognized with the Emissions Energy Project of the Year award at the 8th Annual Platts Global Energy Awards held Thursday night in New York. GreenFuel’s Emissions-to-Biofuels™ technology uses an algae bioreactor system connected to the smokestack of APS' Redhawk 1,040 megawatt power to recycle carbon dioxide emissions, thereby reducing the amount of CO2 dispersed into the air, and then converts the algae into renewable biofuels.
The emissions to biofuels project addresses two important issues in the U.S. today — reducing greenhouse gas emissions at power plants and producing more domestic sources of alternative fuels for automobiles and power plants. Theoretically, this is the first step in creating a self-sustaining renewable energy system for producing electricity.
At Redhawk, the CO2 emissions are trapped and transferred to specialized containers, shown above, holding algae. In the presence of sunlight, the algae consume the CO2 and multiply. Once enough algae is grown, it is harvested, and its starches are turned into ethanol; its lipids into biodiesel; and its protein into high-grade food for livestock or returned to the algae farm as nutrients. It is estimated that for every acre of algae grown on the plant site, up to 150 tons of CO2 can be absorbed — the greatest ever achieved outside of a laboratory.
"This is the first time ever that algae biomass created on-site by direct connection to a commercial power plant has been successfully converted to both these biofuels," said Isaac Berzin, GreenFuel's founder and Chief Technology Officer. "The conversion and certification of the fuels were conducted by respected, independent laboratories."
“We estimate that this process can absorb as much as 80 percent of CO2 emissions during the daytime at a natural gas fired power plant,” said GreenFuel CEO Cary Bullock.
The next phase of study is the construction of an Engineering Scale Unit that will be completed in first quarter of 2007. Construction is about to begin on a series of greenhouselike buildings which will total 30 feet wide by 500 feet long next to the Redhawk station. The algae will be grown at the floor level of the structures, Bullock said.
Unlike CO2 for EOR or sequestration, there are no limitations on the markets for biofuels, and no additional infrastructure requirements to integrate them into the existing transportation markets.
A more detailed description of the bioreactor process is: Flue gas or other CO2-rich gas streams are introduced to the bioreactor, in which algae are suspended in a media with nutrients added to optimize the growth rate. A portion of the media is withdrawn continuously from the bioreactor and sent to dewatering to harvest the algae. The dewatering operation uses two stages of conventional processing. Primary dewatering increases the algae concentration by a factor of 10-30. Secondary dewatering further increases the algal solids concentration to yield a cake suitable for downstream processing. Water removed from the dewatering steps is returned to the bioreactor, with a small purge stream to prevent precipitation of salts. Make-up water is added to maintain the media volume. A blower pulls the flue gas through the bioreactor. Using an induced draft fan provides several operating advantages, including ensuring minimal disruption to power plant operations, simplifying retrofits to existing facilities. (more details about their process can be found here)
The process steps from the flue gas inlet through end of dewatering comprise the "front end" of the GFT process. The unit operations for algal oil extraction and conversion of the dewatered algae into final fuel products is the "downstream processing" portion of the flow sheet. In contrast to the front-end unit operations, the downstream processes are conventional technologies currently practiced on a large scale, e.g. biodiesel is currently produced from vegetable oils via transesterification (several algae species have lipids, starch, and protein compositions similar to soy and canola beans). Consequently the same facilities can be adapted to produce biodiesel from algae and conventional agricultural feeds.
According to GreenFuel other possible downstream processes include fermentation into ethanol, anerobic digestion to produce methanol, gasification to produce hydrogen or synthesis gas and drying to produce a solid biomass.